Display device with a transparent optical filter

ABSTRACT

Optical filler which is adapted to prevent the reflection of external light and improve a signal level of a signal sent from a display device by preventing attenuation thereof, and which is further adapted to prevent a change in hue of an image and to improve the hue, contrast and brightness of an image, thereby enhancing visibility. First, a liquid crystal display device ( 1 ) outputs light which is linearly polarized light. First linearly polarizing plate ( 2 ) is mounted in the filler in such a manner as to be adjusted to an axis of polarization of the linearly polarized light. Namely, the light outputted from the liquid crystal display device ( 1 ) passes through the first linearly polarizing plate ( 2 ) without being changed. The light passing through the first linearly polarizing plate ( 2 ) is then changed by a first quarter-wave phase difference plate ( 11 ) into circularly polarized light so that the phase difference between extraordinary light and ordinary light is (1/4) of the wavelength. Subsequently, light passes through a transparent touch panel ( 12 ) and further propagates through a second quarter-wave phase difference plate ( 7 ). At that time, a phase difference therebetween is caused by (−1/4) of the wavelength of the light in which the phase difference of (1/4) of the wavelength has been caused. Thus, when passing through the touch panel( 12 ), the light is changed into linearly polarized light. Then, the light, which has propagated through the transparent touch panel ( 12 ) and the second quarter-wave phase difference plate ( 7 ), passes through the second linearly polarizing plate ( 6 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an optical filter mounted onthe screen of a display adapted to emit linearly polarized light and,more particularly, to an optical filter disposed on a transparent touchpanel or the like, which is mounted on a liquid crystal displayapparatus.

2. Description of the Related Art

In recent years, among portable information devices such as a personaldigital assistant (PDA), an electronic notebook (or pocketbook), a wordprocessor, a notebook personal computer and a remote control device, acar navigation system, a bank terminal (for example, a cash dispenser),Internet Kiosks, and office automation (OA) equipment (for instance,point-of-sales (POS) terminals, facsimile (FAX) and copying machines),such devices of the type that utilize liquid crystals have been inincreasing demand. Moreover, such devices of the type that furtherutilize transparent touch panels have been on the increase.

There have been the following three types of conventional transparenttouch panels which are classified according to the kinds of materials oftwo composing layers thereof:

(α) (Film+Film) type;

(β) (Film+Glass) type; and

(γ) (Glass+Glass) type.

Method of preventing the reflection of external light (or ambient light)to be employed by each of such conventional transparent touch panels isdetermined in accordance with the material (film or glass) of anoperating section (or layer). Thus, the conventional transparent touchpanels will be described hereinbelow by being classified according tothe material of the operating section thereof.

First, the case, in which the material of the operating section of atouch panel is a film (namely, is of the aforementioned type (α) or(β)), will be described hereunder. As the method of preventing thereflection of external light, there have been developed a method ofperforming a non-glare treatment on the surface of a film of theoperating section, and another method of applying AR (anti-reflective)coating to the surface of a film of the operating section.

(i) In the case of employing the method of performing the non-glaretreatment on the surface of the film of the operating section, externallight is dispersed or scattered by embossing, printing and applying acoating thereon and thus realizing a rugged surface of the film of theoperating section.

(ii) Further, in the case of applying AR coating on the surface of thefilm of the operating section, the film is coated with a large number oflayers respectively made of materials, such as SiO₂ and MgF₂ which aredifferent in refractive index from one another. Thus, the reflection ofexternal light in a visible range can be prevented. This utilizes theproperties that the reflection of light occurs on the boundary surfaceof a substance and that when the light is incident from a substancehaving a small refractive index upon another substance having a largerefractive index.

Next, the case, in which the material of the operating section is glass(namely, the aforementioned type (γ), will be described hereinbelow. Inthis case, as the method of preventing the reflection of external lighton the touch panel, there have been devised a method of etching thesurface of glass of the operating section, a method of sticking aspecial film to the surface of a glass layer of the operating section, amethod of applying AR coating to the surface of glass of the operatingsection and a method of affixing an ordinary (non-polarizing) filter tothe surface of the operating section.

(iii) In the case of the method of etching the surface of a glass layerof the operating section, external light is dispersed by realizing anuneven surface of the glass layer by etching thereof. This methodutilizes similar properties as utilized in the case (i).

(iv) In the case of sticking a special filter to the surface of theglass layer of the operating section, a protecting film, the surface ofthe glass layer of which undergoes an embossing and a non-glaretreatment, is stuck thereto. This method is similar to a method ofsticking a smoke sheet (or film) to a window of a vehicle.

(v) In the case of the method of applying AR coating to the surface ofthe glass layer of the operating section, the glass layer of theoperating section is coated with a large number of stacked layers whichare different in refractive index from one another, similarly as in theaforementioned case (ii). Thus, the reflection of light in the visiblerange is prevented.

(vi) In the case of affixing an ordinary filter to the surface of theoperating section, external light reflected by the surface of the glasslayer of the operating section is return light. Thus, if thetransmittance (or transmissivity) of the ordinary non-polarizing filteris 40%, the intensity of the reflected light is obtained by0.4×0.4=0.16, and is, therefore, attenuated.

In addition to the aforementioned methods, in the case that the materialof the operating section (namely, in the aforementioned case (γ), therehave been developed a method of using a linearly polarizing plate, and amethod of using a circularly polarizing plate which is a combination ofa linearly polarizing plate and a phase difference plate.

(vii) Method of using the linearly polarizing plate is to prevent thereflection of external light by sticking the linearly polarizing plateto the surface of the glass layer of the operating section.

FIG. 11 schematically shows the configuration of a transparent touchpanel using a linearly polarizing plate, which is mounted on the screenof a liquid crystal display device (LCD). Linearly polarizing plate 6 isstuck to the surface of a glass layer (an upper tin doped indium oxide(ITO) glass layer) of the operating section 4.

Transmissivity of the linearly polarizing plate 6 is usually not morethan 45%. Thus, the intensity of the reflected light is obtained byo.45×0.45≈0.2, namely, attenuated in such a manner as to become not morethan 0.2.

(viii) Method of using the circularly polarizing plate, a combination ofa linearly polarizing plate and a phase difference plate is stuck to theglass layer of the operating section. Thus, the reflection of externallight is prevented.

FIG. 12 schematically shows the configuration of a transparent touchpanel using a circularly polarizing plate, mounted on the screen of aliquid crystal device.

Circularly polarizing plate 8 is stuck to a glass layer (namely, anupper ITO glass layer) 4. Circularly polarizing plate 8 is a combinationof a linearly polarizing plate 6 and a quarter-wave phase differenceplate 7. Quarter-wave phase difference plate 7 is stuck onto the glasslayer 4 of the operating section. Moreover, another linearly polarizingplate 6 is stuck thereon.

With such a configuration, external light is changed into linearlypolarized light, the electric field vector of which lies along Y-axis,after passing through the linearly polarizing plate 6. Next, if thislinearly polarized light is divided into a vibration in an optical axisZ of the phase difference plate and a vibration and a vibration inZ-direction of an orthogonal axis Y. these vibrations coincide with anextraordinary ray and an ordinary ray propagating a doubly refractingelement or crystal, respectively. Thus, after passing through the phasedifference plate 7, the phase difference between waves vibrating inY-direction and Z-direction, respectively, is (¼)-wavelength (namely,the linearly polarized light is changed into circularly polarizedlight). Part of light having passed through the circularly polarizingplate 8 is reflected by the surface of the touch panel. Then, the phasedifference plate 7 causes again a phase difference of (¼)-wavelengthbetween the waves vibrating in Y-direction and Z-direction,respectively, to which return light acting as the reflected light isdivided. Consequently, a total phase difference between the wavesvibrating in Y-direction and Z-direction, respectively, into which thereflected light is divided, is (½)-wavelength after passing through thephase difference plate 6, in comparison with the case that there is nophase difference between those into which the initial external lightbeing incident upon the plate 6 is divided.

Linearly polarized light, the plane of vibration of which lies inZ-direction, is synthesized from two light waves, the phase differencebetween which is (½)-wavelength. Plane of polarization of this linearlypolarized light is orthogonal to Y-direction. Thus, the light havingpassed through the phase difference plate 7 cannot further pass throughthe linearly polarizing plate 6 (in the upward direction).

Thus, the reflection of external light can be prevented by thecircularly polarizing plate 8.

The aforementioned conventional methods, however, have the followingproblems.

First, in the case of the conventional methods described in theforegoing descriptions (i), (iii) and (iv), the degree of non-glareeffects is enhanced so as to realize a rugged surface of the film or theglass layer, an image is blurred owing to the relation between the pixelsize and pitch of liquid crystal display device. If the degree ofnon-flare effects is further enhanced, the displaying surface of thedevice becomes clouded due to the brightness of external light.Consequently, an image becomes hard to observe.

Further, if the diffuse reflectance of the surface of the film or glasslayer is increased, the transmissivity thereof is decreased. Moreover,it is necessary for enhancing the brightness of an image to raise thebrightness of backlighting light in the liquid crystal display device.This, however, results in increase in the power consumption of thedevice and in reduction in the life of a source of backlighting.Furthermore, even if the reflection of external light can be prevented,light cannot be prevented from being reflected by the inside (namely,ITO layer and the glass layer) of the touch panel. Thus, the visibilitycannot be improved.

Further, in the case of the conventional methods described in theaforementioned descriptions (ii) and (v), AR coating is applied to thesurface of the film and glass layer of the operating section by coatingthe surface thereof with two to five layers of substances which aredifferent in refractive index from one another. However, such methodshave the following defects. Surfacial hardness of the coating is low, sothat the surface of the film and glass layer is fragile. Additionally,some materials of the surface coating have low chemical resistance.Surface of the coating is easily affected by chemicals.

Further, in the case of these methods, even when the reflection ofexternal light can be prevented, light reflected by the inside (namely,ITO layer and the glass layer) of the touch panel cannot be prevented.Thus, the visibility can not be enhanced.

Moreover, in the case of the method described in the foregoingdescription (vi), the reflectance can be restrained to some extent bysticking a non-polarizing filter to the surface of the film or glasslayer. However, the transmissivity of the non-polarizing filter is low.This method, thus, has defects in that the lightness of an image islowered and that the visibility is lowered in light environment.

In the case of the method described in the foregoing description (vii),the transmissivity corresponding to the linearly polarizing plate is 30to 45%. Thus, an amount of the reflected light is decreased by areduction in an amount of incident external light, which is caused byusing a linearity polarizing plate. However, components of a signal sentfrom a liquid crystal display device are attenuated. Thus, thevisibility of an image is degraded.

In the case of the method described in the foregoing description (viii),a circularly polarizing plate obtained by combining a linearlypolarizing plate with a phase difference plate is used. Thus, thetransmissivity of the circularly polarizing plate is decreased in such amanner as to be lower than that of the linearly polarizing device. Thebrightness or lightness of an image is decreased as the transmissivityis lowered. Moreover, the visibility in light environment is degraded.Furthermore, the hue of an image is changed by the circularly polarizingplate.

The present invention is accomplished to solve the aforementionedproblems of the prior art.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an opticalfilter which prevents the reflection of external light and improves bypreventing a reduction in signal level of a signal sent from a displaydevice and prevents change in hue of an image and enhances thevisibility by improving the hue, the contrast and the brightness.

To achieve the foregoing object, in accordance with an aspect of thepresent invention, there is provided an optical filter (hereundersometimes referred to as a first optical filter of the presentinvention), which is mounted on a display device adapted to emitlinearly polarized light, and comprises: a non-polarizing orlowly-polarizing member; a linearly polarizing plate; and first andsecond phase difference plates, wherein the aforesaid linearlypolarizing plate and the aforesaid second phase difference plate preventthe reflection of external light which has passed through the aforesaidlinearly polarizing plate and the aforesaid second phase differenceplate and has been incident on the aforesaid display device, whereinlight sent from the aforesaid display device is adapted in such a manneras to pass through the aforesaid second phase difference plate and theaforesaid linearly polarizing plate after passing the aforesaid firstphase difference plate, and wherein an amount of a phase change causedby the aforesaid first and second phase difference plates is set so thatthe light sent from the aforesaid display device passes through theaforesaid linearly polarizing plate during the light is in an opticallybest state.

Thus, optical characteristics, such as the visibility, of the displaydevice can be extremely enhanced.

In the case of an embodiment (hereunder sometimes referred to as asecond optical filter of the present invention) of the first opticalfilter of the present invention, the aforesaid first and second phasedifference plates are placed so that phase differences respectivelycaused by the aforesaid first and second phase difference plates arecanceled, thereby enhancing the transmissivity.

In the case of an embodiment (hereunder sometimes referred to as a thirdoptical filter of the present invention) of the first or second opticalfilter of the present invention, the aforesaid first and second phasedifference plates are quarter-wave phase difference plates.

In the case of an embodiment (hereunder sometimes referred to as afourth optical filter of the present invention) of one of the first tothird optical filler of the present invention, the aforesaidnon-polarizing or low-polarizing member is made of a high-polymer orglass.

In the case of an embodiment (hereunder sometimes referred to as a fifthoptical filter of the present invention) of one of the first to fourthoptical filter of the present invention, the aforesaid non-polarizing orlow-polarizing member is shaped like a plate or film.

In the case of an embodiment (hereunder sometimes referred to as a sixthoptical filter of the present invention) of one of the first to fifthoptical filter of the present invention, the aforesaid display device isa liquid crystal display device.

In the case of an embodiment (hereunder sometimes referred to as aseventh optical filter of the present invention) of one of the first tosixth optical filter of the present invention, which is of ahermetically sealed structure, which is filled with inert gases.

In accordance with another aspect of the present invention, there isprovided an optical filter (hereunder referred to as an eighth opticalfilter of the present invention) which comprises: a display device; atransparent touch panel device mounted on the screen of the aforesaiddisplay device, wherein a second linearly polarizing plate and a secondquarter-wave phase difference plate are provided on the surface of theaforesaid touch panel device in sequence, and wherein a firstquarter-wave phase difference plate is provided in such a way as to beinterposed between the aforesaid display device and the aforesaidtransparent touch panel device.

In the case of an embodiment (hereunder sometimes referred to as a ninthoptical filter of the present invention) of the eighth optical filter ofthe present invention, which further comprises: a first linearlypolarizing plate interposed between the aforesaid display device and thefirst quarter-wave phase difference plate.

In the case of an embodiment (hereunder sometimes referred to as a tenthoptical filter of the present invention) of the eighth or ninth opticalfilter of the present invention, wherein the aforesaid second linearlypolarizing plate and the aforesaid second quarter-wave phase differenceplate are stacked in such a manner as to be integral with each other andform a layered element, and wherein this layered element is bonded orfixed to the aforesaid transparent panel device by interposing bondingmeans or a spacer between a part of the aforesaid layered element facinga peripheral portion of the aforesaid transparent touch panel device,which is other than an operating section of the aforesaid transparenttouch panel device, and the aforesaid peripheral portion of theaforesaid transparent touch panel device. In the case of an embodiment(hereunder sometimes referred to as an eleventh optical filter of thepresent invention) of the tenth optical filter of the present invention,the aforesaid bonding means is a pressure sensitive adhesive doublecoated film.

In the case of an embodiment (hereunder sometimes referred to as atwelfth optical filter of the present invention) of one of the eighth toeleventh optical filters of the present invention, the aforesaid displaydevice is a liquid crystal display device.

In the case of an embodiment (hereunder sometimes referred to as athirteenth optical filter of the present invention) of the twelfthoptical filter of the present invention, the aforesaid liquid crystaldisplay device is of the polymer dispersed type. In the case of anembodiment of the twelfth or thirteenth optical filter of the presentinvention, a single member is adapted to serve as two or more of apartof the aforesaid transparent panel device, the aforesaid first phasedifference plate and the aforesaid liquid crystal display device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparent from the following description of preferred embodimentswith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout several views, and inwhich:

FIG. 1 is a schematic diagram illustrating the configuration of anoptical filter which is an embodiment of the present invention;

FIG. 2 is a diagram illustrating the relation between the mountingangles of the linearly polarizing plate and the phase difference plateof the optical filter of the embodiment of the present invention;

FIG. 3 is a diagram illustrating the configuration of a conventionaltransparent touch panel of the film type and the reflection of lighttherein;

FIG. 4 is a diagram illustrating the configuration of a conventionaltransparent touch panel of the glass type and the reflection of lighttherein;

FIG. 5 is a diagram illustrating the configuration of an optical filteraccording to the embodiment of the present invention and the reflectionof light therein;

FIG. 6 is a table for the comparison of the brightness Y-value and thehue Δ a * b * between a conventional example and the embodiment of thepresent invention;

FIG. 7 is a diagram illustrating angles of field of the conventionalexample and the embodiment of the present invention;

FIG. 8 is a diagram illustrating the configuration of an optical filterof “Example 1” of the present invention;

FIG. 9 is a diagram illustrating the configuration of an optical filterof “Example 2” of the present invention;

FIG. 10 is a diagram illustrating the configuration of an optical filterof “Example 3” of the present invention;

FIG. 11 is a diagram schematically illustrating the configuration of atransparent panel using a conventional linearly polarizing plate;

FIG. 12 is a diagram schematically illustrating the configuration of atransparent panel using a conventional circularly polarizing plate;

FIG. 13 is a diagram illustrating the configuration of an optical filterof “Example 4” of the present invention;

FIG. 14 is a diagram illustrating the configuration of an optical filterof “Embodiment 5” of the present invention; and

FIG. 15 is a diagram illustrating a modification of “Example 5” of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, optical filters according to the present invention, whichare embodiments of the present invention, will be described in detail byreferring to the accompanying drawings.

FIG. 1 schematically shows the configuration of the optical filter whichis this embodiment of the present invention. Incidentally, thisembodiment is an example of application of the present invention to aliquid crystal display device provided with a touch panel device.

Liquid crystal display device 1 is usually equipped with first linearlypolarizing plate 2. Further, a circularly polarizing plate 8, which is acombination of a second linearly polarizing plate 6 and a secondquarter-wave phase difference plate 7, is mounted on a plate-like orfilm-like member made of polymer or glass of the operating section 10.

Most characteristic aspect of the present invention resides in that theoptical filter of the present invention is provided with a firstquarter-wave phase difference plate 11 in addition to the aforementionedcomposing elements. Light rays outputted from the liquid crystal display(LCD) device 1 are linearly polarized light rays, and the first linearlypolarizing plate 2 is mounted thereon in such a manner as to be adjustedto the axis of polarization of the linearly polarized light. Namely,light rays outputted from the liquid crystal display device 1 passesthrough the first linearly polarizing plate 2 without being changed.

FIG. 2 shows the relation among the mounting angles of the first andsecond linearly polarizing plates 2 and 6 and the phase differenceplates 7 and 11. Further, the second quarter-wave phase difference plate7 and the first quarter-wave phase difference plate 11 are placed sothat the difference between the mounting angles of the plates 7 and 11is 90°.

Light rays having passed through the first linearly polarizing plate 2without being altered is changed by the first quarter-wave phasedifference plate 11 into (circularly polarized) light rays in which thephase difference between an extraordinary light ray and an ordinarylight ray is (¼) of the wavelength. Subsequently, light rays havingpassed through the transparent touch panel 12 propagates through thesecond quarter-wave phase difference plate 7. At that time, a phaseshift or difference of (−¼) of the wavelength is caused between theextraordinary light ray and the ordinary light ray, the phases of whichhave been previously made to be different from each other by (¼) of thewavelength thereof. Thus, the light ray having passed through the secondquarter-wave phase difference plate 7 becomes linearly polarized lightray.

Light ray, which has been thus changed into linearly polarized light bypassing through the transparent touch panel 12 and the secondquarter-wave phase difference plate 7, passes through the secondlinearly polarizing plate 6. In the case of this embodiment, the causedphase differences are canceled by using two quarter-wave phasedifference plates 11 and 7. Thus, light, which is incident upon thesecond linearly polarizing plate 6 from the liquid crystal displaydevice 1, does not include a component thereof in a direction orthogonalto the axis of polarization of the second linearly polarizing plate 6.Conventional system is not provided with the quarter-wave phasedifference plate 11. Thus, light, which is incident upon the secondlinearly polarizing plate 6 from the liquid crystal display device 1,includes a component thereof in a direction orthogonal to the axis ofpolarization of the second linearly polarizing plate 6. Further, thisorthogonal component does not pass through the second linearlypolarizing plate 6. Consequently, the visibility of the touch panel isvery low.

FIG. 3 schematically illustrates the configuration of the conventionaltouch panel of the film type (namely, of the type that uses film as theoperating section) and the reflection of external light.

Transmissivity of the touch panel of this type was as follows:

Actually measured value: 81.7% (at 550 nm)

Calculated value: 80.8% (all light)

Thus, about 20% of the light was reflected and absorbed. Further, FIG. 4schematically shows the conventional touch panel of the glass type(namely, of the type using glass in the operating section) and thereflection of external light. Transmissivity of the touch panel of thistype is as follows:

Actually measured value: 85.7% (at 550 nm)

Calculated value: 84.6% (all light)

Thus, about 15% of the light was reflected and absorbed Further, thetransmissivity of the touch panel of the circularly polarizing type,which was obtained by using a circularly polarizing plate in theconventional touch panel of the glass type and taking measures againstexternal light; was 31.1% (calculated value). Thus, about 69% of thelight was reflected and absorbed.

FIG. 5 schematically illustrates a touch panel according to thisembodiment of the (circularly polarizing plate+the phase difference type(namely, of the type that uses glass as the operating section, andfurther employs a circularly polarizing plate) and the reflection ofexternal light:

Actually measured value: 67.4% (at 550 nm)

Calculated value: 72.9% (all light)

Thus, the transmissivity of this type is about 2.2 times that of theconventional circularly-polarizing type.

In the case of this embodiment, the visibility is evaluated by beingdefined as follows:

Visibility=Transmissivity×Reflectance

Incidentally, the visibility in each of the cases of the conventionaltouch panels of the film type, the glass type and the circularlypolarizing type and of the (circularly polarizing plate+the phasedifference plate) type is as follows:

(Circularly- Circularly- Polarizing-Plate + Film Glass Polarizing-Phase-Difference- Type Type Type Plate) Type Transmissivity (%) 80.884.6 31.1 72.9 Reflectance (%) 14.1 15.7 3.0 3.0 Visibility 5.7 5.4 10.424.3As is seen from this table, the visibility is extremely enhanced in thecase of the touch panel of(circularly-polarizing-plate+phase-difference-plate) type according tothis embodiment. FIG. 6 shows the visibility (namely, the brightnessY-value nd the hue Δ a * b * ) when the touch panel of this mbodiment isviewed from four directions (namely, from above, below, left and right)and at inclination angles of 0, 10, 22, 34, 41 and 57° corresponding toeach of the four directions. Incidentally, regarding the hue in the caseof front visibility, the color difference Δ a * b * is used as aparameter corresponding to the hue, because the chromaticity a *=0 and b*=0 indicate achromatic color. As shown in FIG. 6, the brightness ishigh and the hue changes little over a wide range. Moreover, regardlessof the inclination angle, a change to same hue occurs. Referring next toFIG. 7, there are shown angles of field in the cases of the conventionaltouch panels of the film type, the glass type and the circularlypolarizing type and of the (circularly polarizing plate+the phasedifference plate) type, for the purpose of comparison therebetween.Incidentally, the angle of field was measured by assuming that an objectis visible in the case where Y-value is more than 40% and the colordifference is less than 30%, as a reference for the measurement. It isapparent from this figure that, in the case of this embodiment, anglesof field is large in comparison with the conventional touch panels thefilm type, the glass type and the circularly polarizing type.

EXAMPLE 1

FIG. 8 schematically illustrates the configuration of an optical filterwhich is “Example 1” of the present invention. This is an example ofapplication of the present invention to a liquid crystal display deviceprovided with a touch panel. Transparent touch panel used in thisexample is of the type(γ), namely, (Glass+Glass)type. Visibility of thisexample is enhanced by using the circularly polarizing plate 8 (namely,a combination of the second linearly polarizing plate 6 and the secondphase difference plate 7) and the first phase difference plate 11.Furthermore, the first linearly polarizing plate 2 is preliminarilymounted on the liquid crystal display device 1. Incidentally, thefollowing materials are used in this example.

Circularly Polarizing Plate 8:

Material of a second (dye based) linearly polarizing plate 6:

ST-1822AP-AG3

 manufactured by Sumitomo Chemical Company Limited

Material of a second phase difference plate 7:

SEF-¼ λ

 manufactured by Sumitomo Chemical Company Limited

Material of Transparent Touch Panel:

Glass3, 4

manufactured by DOWA VISUAL SYSTEM CO., LTD

Material of First Phase Difference Plate 11:

SEF-¼ λ

manufactured by Sumitomo Chemical Company Limited

Reflection of external light by the surface of ITO layer 5 and glasslayers 3 and 4 is prevented by the circularly polarizing plate 8 mountedon the upper portion of the optical filter. Moreover, a reduction in thetransmissivity and a change in the hue can be prevented by the firstphase difference plate 11 mounted on the lower glass layer 3.

EXAMPLE 2

In the case of this example, a polycarbonate film is used instead of theupper glass layer 4 of “Example 1”. To obtain a polycarbonate filmhaving low polarization, the polycarbonate film is produced by a castingmethod. FIG. 9 illustrates the configuration of a touch panel of thisexample.

Transparent touch panel used in this example is of the type(β), namely,(Film+Glass)type. Visibility of this example is enhanced by using thecircularly polarizing plate 8 (namely, a combination of the secondlinearly polarizing plate 6 and the second phase difference plate 7) andthe first phase difference plate 11. Furthermore, the first linearlypolarizing plate 2 is preliminarily mounted on the liquid crystaldisplay device 1. Incidentally, the following materials are used in thisexample.

Circularly Polarizing Plate 8:

Material of a second (dye based) linearly polarizing plate 6:

ST-1822AP-AG3

manufactured by Sumitomo Chemical Company Limited

Material of a second phase difference plate 7:

SEF-0096 (Phase Difference 96 nm)

manufactured by Sumitomo Chemical Company Limited

Material of Transparent Touch Panel:

Film 13+Glass 3

manufactured by DOWA VISUAL SYSTEM CO., LTD

Polycarbonate film 13 (phase difference: 40 to 50 nm)

Material of First Phase Difference Plate 11:

SEF-¼ λ

manufactured by Sumitomo Chemical Company Limited

Incidentally, this example is designed so that the total phasedifference caused by the second phase difference plate 7 and thepolycarbonate film 3 is equal to (¼) of the wavelength. Namely, thedegree of polarization of the polycarbonate film 13 is very low.However, the polycarbonate film 13 exhibits the polarizationcorresponding to a phase difference of 40 to 50 nm. First phasedifference plate causes a phase difference corresponding to (¼) of thewavelength. Thus, if a phase difference plate causing a phase differencecorresponding to (¼) of (he wavelength is used as the second phasedifference plate 7, there occur subtle changes in optical properties,such as the hue and the transmissivity. To eliminate an error, theposition of the second phase difference plate 7 is regulated. Moreover,the total phase difference caused by the second phase difference plate 7and the polycarbonate film 13 is made to be equal to (¼) of thewavelength. This example can obtain advantageous effects similar tothose of “Example 1”.

EXAMPLE 3

This example is obtained by removing the first linearly polarizing platefrom each of “Example 1” and “Example 2”. Namely, the first linearlypolarizing plate mounted on the liquid crystal display device isomitted. Instead of this first linearly polarizing plate, the secondlinearly polarizing plate composing the circularly polarizing plate isused. Thus, the second linearly polarizing plate has the anti-reflectionfunction and the functions of the first linearly polarizing plateusually mounted on the liquid crystal display device. FIG. 10 shows theconfiguration of this “Example 3”. Further, there are two kinds ofmodifications of this “Example 3”, namely, (Glass+Glass) type and(Film+Glass) type. Incidentally, this example of the (Glass+Glass) typeuses the following materials.

Circularly Polarizing Plate 8:

Material of a second (dye based) linearly polarizing plate 6:

ST-1822AP-AG3

manufactured by Sumitomo Chemical Company Limited

Material of a second phase difference plate 7:

SEF-¼ λ

manufactured by Sumitomo Chemical Company Limited

Material of Transparent Touch Panel:

Glass3, 4

manufactured by DOWA VISUAL SYSTEM CO., LTD

Material of First Phase Difference Plate 11:

SEF-¼ λ

manufactured by Sumitomo Chemical Company Limited

Moreover, this example of the (Film+Glass) type uses the followingmaterials.

Circularly Polarizing Plate 8:

Material of a second (dye based) linearly polarizing plate 6:

ST-1822AP-AG3

manufactured by Sumitomo Chemical Company Limited

Material of a second phase difference plate 7:

SEF-0096 (Phase Difference 96 nm)

manufactured by Sumitomo Chemical Company Limited

Material of Transparent Touch Panel:

Film13+Glass 3

manufactured by DOWA VISUAL SYSTEM CO., LTD

-   -   Polycarbonate film 13 (phase difference: 40 to 50 nm)

Material of First Phase Difference Plate 11:

SEF-¼ λ

manufactured by Sumitomo Chemical Company Limited

This example can obtain advantageous effects similar to those of“Example 1” and “Example 2”. In addition, the manufacturing cost can bereduced by omitting the first linearly polarizing plate 2.Simultaneously, the transmissivity can be enhanced.

EXAMPLE 4

FIG. 13 is a diagram schematically showing the configuration of anoptical filter which is “Example 4”. This example is obtained by bondingand fixing only the peripheral portion of the circularly polarizingplate 8 of “Example 3” onto the upper ITO glass layer of the transparenttouch panel by the use of pressure sensitive adhesive double coated tape20. As shown in FIG. 13, the double coated tape 20 is interposed betweena portion of the circularly polarizing plate 8, which faces a peripheralportion of the upper ITO glass layer 4 other than the operating sectionthereof, and the peripheral portion of the upper ITO glass layer 4,which is other than the operating section. Thus, the circularlypolarizing plate 8 is bonded and fixed to the upper ITO glass 4. In thecase of this example, only the peripheral portion thereof other than theoperating section is bonded and fixed. Thus, as compared with theconventional case where the entire surface of the polarizing plate isbonded and fixed, this example causes no problems even if foreignsubstances are mixed into the bonding portion. Moreover, even in thecase that foreign substances enters the operating section, thedisassembly thereof is relatively easily performed. Therefore, theremoving of the foreign substances is relatively easily achieved.Incidentally, a spacer member may be used in place of the double coatedtape, and further, a mechanism for nipping this spacer member and fixingthe spacer member mechanically maybe provided in a modification of thisexample.

EXAMPLE 5

FIG. 14 schematically shows the configuration of an optical filter whichis “Example 4”. This example is adapted so that a single member performsthe functions of the lower ITO glass layer 3 of the transparent touchpanel, the first phase difference plate 11 and the upper glass layer ofthe liquid crystal display device 1 of “Example 3”. As shown in FIG. 14,a general-purpose member 130, on the surface of which ITO film 5 isformed in such a way as to face the upper ITO glass layer 4, isprovided. This general-purpose member 130 serves as an upper glass layerwhich sandwiches a liquid crystal portion 10 together with a lower glasslayer 120 and thus composes a liquid crystal cell portion. In this case,the general-purpose portion 130 further performs the function of thefirst phase difference plate. This general-purpose member 130 isconstituted by, for example, providing a phase difference plate 131 on aglass plate 132 as illustrated in FIG. 15. Needless to say, thegeneral-purpose member 130 may be constituted by a phase differenceplate made of a transparent polymer material. Incidentally, the lowerpolarizing plate 140, and a backlighting portion 150 are mounted on thelower glass layer 120, sequentially. In the case of this example, thefunctions of the lower glass layer of the touch panel, the phasedifference plate and the upper glass layer of the liquid crystal displaydevice are performed by a single member. As compared with the case thatthese functions are performed by separated members, the transmissivityand the surface reflection can be reduced by amounts corresponding tothe separated members. Furthermore, the visibility can be considerablyenhanced. In addition, the entire structure of the optical filter can besimplified. Consequently, this example is very advantageous formanufacturers to reduce the manufacturing cost.

Other Embodiments

The present invention is not limited to the aforementioned embodiment.Various modification and alteration are allowed.

In the aforesaid embodiments, glass and polycarbonate film are used asthe materials of the transparent touch panel. However, other materialsmay be used as long as having no polarization or a low degree ofpolarization. Further, the mounting angles of the phase difference plateand the linearly polarization plate are not limited to those illustratedin FIG. 2. Other angles may be employed as the mounting angles.

Further, to enhance the stability and the visibility, the transparenttouch panel may be perfectly hermetically scaled and may be filled withinert gases. Moreover, as long as outputting linearly polarized light,any other display device other than a liquid crystal display device maybe used as the display device. In the case of applying a liquid crystaldisplay device, needless to say, what are called TFT liquid crystal, STNliquid crystal and TFT liquid crystal may be employed as liquid crystalsof the liquid crystal display device. Especially, if using the polymerdispersed type liquid crystals, the use of polarizing plates in theliquid crystal display device itself is not always needed. Therefore,the visibility is further enhanced owing to the multiplier effects ofthe present invention and the liquid polymer dispersed type.Furthermore, the structure of the optical filter can be furthersimplified, The present invention can be applied to devices other thanthe transparent touch panel (and the optical filter), similarly. Forexample, a display window for a dust-proof case, and a protecting filterfor a display device.

Although the preferred embodiments of the present invention have beendescribed above, it should be understood that the present invention isnot limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the spirit of theinvention.

The scope of the present invention, therefore, is to be determinedsolely by the appended claims.

1. A display apparatus, comprising: a display device adapted to emitlinearly polarized light; a transparent optical device mounted on saiddisplay device, said transparent optical device comprising anon-polarizing or low-polarizing member; an anti-reflective layer,comprising a linearly polarizing plate and a phase difference plate,provided on a surface of said transparent optical device; and anotherphase difference plate, provided between said display device and saidphase difference plate of the anti-reflective layer, that imparts aphase difference that cancels a phase difference imparted by said phasedifference plate of the anti-reflective layer.
 2. The display apparatusaccording to claim 1, wherein both of said phase difference plates arequarter-wave phase difference plates.
 3. The display apparatus accordingto claim 1, wherein said non-polarizing or low-polarizing member is madeof a high-polymer or glass.
 4. The display apparatus according to claim1, wherein said non-polarizing or low-polarizing member is shaped like aplate or film.
 5. The display apparatus according to claim 1, whereinsaid display device is a liquid crystal display device.
 6. The displayapparatus according to claim 1, wherein said transparent optical deviceis a hermetically sealed structure that is filled with inert gases.
 7. Adisplay apparatus comprising: a display device having a screen; atransparent touch panel device mounted on the screen of said displaydevice; a first phase difference plate provided between said displaydevice and said transparent touch panel device; a first linearlypolarizing plate provided between said first phase difference plate andsaid display device; and an anti-reflective layer, comprising a secondlinearly polarizing plate and a second phase difference plate, providedon a surface of said touch panel device; and , wherein anothersaid firstphase difference plate provided between said display device and saidtransparent touch panel device that imparts a phase difference thatcancels a phase difference of light emitted from said display deviceimparted by said second phase difference plate of the anti-reflectivelayer.
 8. The display apparatus according to claim 7, further comprisinganother linearly polarizing plate interposed between the display deviceand said another phase difference plate.
 9. The display apparatusaccording to claim 7, wherein said second linearly polarizing plate andsaid second phase difference plate of said anti-reflective layer arestacked in such a manner as to be integral with each other and form alayered element, and wherein said layered element is bonded or fixed tosaid transparent touch panel device by interposing bonding means or aspacer between a part of said layered element facing a peripheralportion of said transparent touch panel device, which is other than anoperating section of said transparent touch panel device, and saidperipheral portion of said transparent touch panel device.
 10. Thedisplay apparatus according to claim 9, wherein said bonding means is anadhesive double coated film.
 11. The display apparatus according toclaim 7, wherein said display device is a liquid crystal display device.12. The display apparatus according to claim 11, wherein said liquidcrystal display device is of the polymer dispersed type.
 13. The displayapparatus according to claim 11, wherein a transparent member composingsaid transparent touch panel device comprises said another first phasedifference plate.
 14. The display apparatus according to claim 7,wherein said transparent touch panel device comprises non-polarizing orlow-polarizing member.
 15. The display apparatus according to claim 7,wherein said second phase difference plate attaches directly to asurface of said touch panel device.
 16. The display apparatus accordingto claim 14, wherein said second linearly polarizing plate and saidsecond phase difference plate of said anti-reflective layer are stackedin such a manner as to be integral with each other and form a layeredelement, and wherein said layered element is bonded or fixed to saidtransparent touch panel device by interposing bonding means or a spacerbetween a part of said layered element facing a peripheral portion ofsaid transparent touch panel device, which is other than an operatingsection of said transparent touch panel device, and said peripheralportion of said transparent touch panel device.
 17. The displayapparatus according to claim 16, wherein said bonding means is anadhesive double coated film.
 18. The display apparatus according toclaim 14, wherein said display device is a liquid crystal displaydevice.
 19. The display apparatus according to claim 18, wherein saidliquid crystal display device is of the polymer dispersed type.
 20. Thedisplay apparatus according to claim 18, wherein a transparent membercomposing said transparent touch panel device comprises said first phasedifference plate.